As is known in the art, phased array antennas are comprised of a plurality of antenna elements or radiators. As is also known, in the design of such antenna elements, a trade-off must typically be made between an operating frequency bandwidth characteristics and cross-polarization isolation characteristics. For example, with proper design, an array of dipole elements can be provided a relatively high cross-polarization isolation characteristics in all scan planes; however, bandwidth is limited. On the other hand, array antennas provided from notch radiators or Vivaldi radiators (for example) are capable or operating over a relatively wide frequency bandwidth, but have a relatively low cross-polarization isolation characteristic off the principal axes.
Droopy bowtie elements disposed above a ground plane are a well known means for producing nominally circular polarized (CP) reception or transmission radiation patterns at frequencies from VHF to microwave wavelengths. Droopy bowtie elements are often coupled to a balun which is realized in a co-axial configuration involving separate subassemblies for achieving balun matching and arm phasing functions. Such a design typically results in an integrated antenna-balun assembly having good bandwidth but a poor cross-polarization isolation characteristic. Furthermore, such a design is relatively difficult to assemble (high recurring engineering cost) and cannot easily be adapted to different operating frequencies or polarizations (high non-recurring engineering cost).
It would, therefore, be desirable to provide an integrated antenna element and for use in a phased array antenna which has good wideband RF performance, good cross-polarization isolation characteristics, and which reduces both recurring and non-recurring engineering costs.